The direct procurement approach
The Australian group, based at St. Vincent’s Hospital in Sydney, developed a technique referred to as “direct procurement”: after the standoff period and declaration of circulatory death, the chest is opened, and the heart is removed. New technology, the Organ Care System (OCS) heart box (Transmedics), is then used to reperfuse and restart the heart outside the body so its suitability for transplant can be assessed.
The heart is kept perfused and beating in the OCS box while it is being transported to the recipient. This has enabled longer transit times than the traditional way of transporting the nonbeating heart on ice.
Peter MacDonald, MD, PhD, from the St Vincent’s group that developed this approach, said, “Most people thought a heart from a DCD donor would not survive transport – that the injury to the heart from the combination of life support withdrawal, stand-off time, and cold storage would be too much. But we modeled the process in the lab and were able to show that we were able to get the heart beating again after withdrawal of life support.”
Dr. McDonald noted that “the recipient of their first human DCD heart transplant using this machine in 2014 is still alive and well.” The Australian group has now done 85 of these DCD heart transplants, and they have increased the number of heart transplant procedures at St. Vincent’s Hospital by 25%.
Normothermic regional perfusion (NRP)
The U.K. group, based at the Royal Papworth Hospital in Cambridge, England, developed a different approach to DCD: After the standoff period and the declaration of circulatory death, the donor is connected to a heart/lung machine using extracorporeal membrane oxygenation (ECMO) so that the heart is perfused and starts beating again inside the body. This approach is known as normothermic regional perfusion (NRP).
Marius Berman, MD, surgical lead for Transplantation and Mechanical Circulatory Support at Papworth, explained that the NRP approach allows the heart to be perfused and restarted faster than direct procurement, resulting in a shorter ischemic time. The heart can be evaluated thoroughly for suitability for transplantation in situ before committing to transplantation, and because the heart is less damaged, it can be transported on ice without use of the OCS box.
“DCD is more complicated than DBD, because the heart has stopped and has to be restarted. Retrieval teams have to be very experienced,” Dr. Berman noted. “This is more of an issue for the direct procurement approach, where the chest has to be opened and the heart retrieved as fast as possible. It is a rush. The longer time without the heart being perfused correlates to an increased incidence of primary graft dysfunction. With NRP, we can get the heart started again more quickly, which is crucial.”
Stephen Large, MBBS, another cardiothoracic surgeon with the Papworth team, added that they have reduced ischemic time to about 15 minutes. “That’s considerably shorter than reperfusing the heart outside the body,” he said. “This results in a healthier organ for the recipient.”
The NRP approach is also less expensive than direct procurement as one OCS box costs about $75,000.
He pointed out that the NRP approach can also be used for heart transplants in children and even small babies, while currently the direct procurement technique is not typically suitable for children because the OCS box was not designed for small hearts.
DCD, using either technique, has increased the heart transplant rate by 40% at Papworth, and is being used at all seven transplant centers in the United Kingdom, “a world first,” noted Dr. Large.
The Papworth team recently published its 5-year experience with 25 NRP transplants and 85 direct procurement transplants. Survival in recipients was no different, although there was some suggestion that the NRP hearts may have been in slightly better condition, possibly being more resistant to immunological rejection.